Travelling wave tube amplifier



June 2l, 1'960 B. EPszTElN TRAVELLING WAVE TUBE AMPLIFIER 2 Sheets-Sheet1 Filed Nov. 13, 1957 June 21, 1960 B. EPszTElN TRAVELLING wAvE: TUBEAMPLIFIER 2 Sheets-Sheet 2 Filed Nov. 15, 1957 United States Patent lrRAvELLiNG WAVE TUBE AMPLIFIER Bernard Epszten, Paris, France, assignerto Compagnie Generale de Telegraphie Sans Fil, Paris, France Filed Nov.13, 1957, Ser. No. 696,118

Claims priority, application France Dec. 4,1956

Claims. (Cl. S15-3.5)

The present invention relates to forward travelling wave amplifiers ofcylindrical structure. More particularly, the present invention relatesto the details of delay lines utilized lin forward wave amplifier tubes.

Helix-type delay lines are already known in the prior art. Moreover, itis known that the travelling wave tubes of the prior artvwhich utilizesuch helix-type delay lines have a relatively large gain and arelatively large bandpass. However, the use of such lines inhigh-powered tubes poses serious problems, particularly as to cooling ofthe delay lines and manner of support or securing thereof which are`rather difficult to resolve. In fact, a helix-type delay line isconstituted by a spirally wound wire of relatively large length; it is,therefore, particularly diicult to cool the spirally wound wire of thehelix-type delay line and tomaintain the same in place since the helix,Le., the spiral turns thereof, are deformed under the action of heat.These inconveniences found in connection with helix-type delay lines ofthe prior art may be reduced, for example, by fixing or securing thehelix at several points thereof, distributed over the entire lengththereof, by means of metallic rods or the like brazed to an externalmetallic tube which is coaxial with respect to the helix. However, as aresult of such rod-like securing means, the width of the band-pass ofthe tube is considerably reduced.

On the other hand, delay line circuits are also already known in theprior art which are constituted by a circular guide provided with andloaded by metallic disks, each including in the center thereof anorifice or aperture for the passage of the electron beam. Such adisk-type delay line circuit is relatively sturdy, and does not offerthe inconveniences and disadvantages of the helix-type delay lineinsofar as .cooling and securing or fastening of the line is concerned;however, tubes which are equipped with delay lines including metallicdisks possess a reduced gain and a relatively small band-pass.

It has already been proposed to solve these difficulties by providing adelay line in the form of a series of ringlike or annular members ofwhich each is connected with a metallic cylinder or guide, surroundingcoaxially the line, by means of n radial rods or spokes forming supportstherefor, with the angular displacement between the supports of eachpair of successive annular members being equal to The United StatesPatent 2,768,322 to Fletcher is representative of this prior art typedelay line.

While this last-described type of line possesses advantages insofar assturdiness and band-pass are concerned in comparison with theaforementioned helix-type delay lines or the dislotype delay lines, thislast-described delay line possesses' an inverse dispersioncharacteristic of the fundamental space wave so that forward waveamplifiers which utilize such type of delay line function or operate bythe interaction with a space harmonic of which the dispersion isforward, and not with the fundamental space wave.

However, tubes utilizing and operating by the interaction with a spaceharmonic other than the fundamental, with all other things remainingequal, have a smaller coupling resistance and a narrower band-pass thantubes operating or functioning by interaction with the fundamental.

Accordingly, the present invention has for its object the provision of adelay line for a forward wave ampliiier which obviates the disadvantagesnoted hereinabove in connection with the prior art devices.

Another object of the present invention is the provision of a delay linefor a forward wave amplifier which is essentially non-dispersive, whichcorresponds to a forward dispersion of the fundamental space harmonicthereof, and which is simultaneously rigid, sturdy and easy -to build.

A still further object of the present invention is the provision of adelay line which readily enables a relatively large dissipation of heatto permit use thereof for high-powered tubes.

Still another object of the present invention is the provision of anamplifier having a large useful band-pass, a large gain and a highpower.

Thus, the present invention has for its object the provision of a delayline which simultaneously conserves the advantage of sturdiness of thedelay line as found in the type of line having annular members asdescribed above, but which, in contradistinction thereto, offers thedesired characteristics of forward dispersion of the fundamental spaceharmonic. By reason of this fact, such delay line is particuiarly usefulin connection with forward wave amplifiers which function or operate byinteraction with the fundamental space wave, and in such applicationthis type of delay line assures a still larger band-pass than theband-pass of the preceding line, and with a larger gain due to therelatively high coupling resistance.

A still further object of the present invention is the provision `of aforward travelling wave amplifier which utilizes such a delay line.

These and other objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connectigLwitl-i the accompanying drawing, which shows, forpurposes of illustration only, several embodiments in accordance withthe present invention, and wherein:

Figure l is an axial longitudinal cross-sectional view through `oneembodiment of a forward wave amplifier tube provided with a delay linein accordance with the present invention taken along line I-I of Figure2;

Figure 2 is a cross-sectional view taken along line II-H of Figure l;

Figure 3 is a cross-sectional view similar to Figure 2 of anotherembodiment of a tube provided with a delay line in accordance with thepresent invention;

Figure 4 is a cross-sectional view similar to Figure 2 of still afurther embodiment of a tube provided with a delay line in accordancewith the present invention, and

Figure 5 is an axial longitudinal cross-sectional view through adifferent embodiment of an amplifier tube in accordance with the presentinvention.

The delay line in accordance with the present invention includes,similar to the line mentioned hereinabove, a metallic guide whichpreferably but not necessarily constitutes the external envelope of thetube, and which includes coaxial metallic ring-like annular members,each secured to the wall of the tube by n radial metallic spokes orrod-like supports, as seen `in cross-sectional views at right angle tothe axis of the tube. However, in contradistinction to theaforementioned known type of delay Patented 'June 2l, i960 line, thedelay line in accordance with the present invention is characterized bythe combination of features that the angular displacement between spokesor rod-like support members of successive ring-like or annular membersis zero and that n metallic filler members are disposed along the innerwall of the tube in the sectors delimited by the radial spoke-likesupport members, which filler members extend over the entire lengthofthe tube and form auxiliary base members of which every section in aplane perpendicular to the axis of the tube has the shape of a sector ofan annulus.

According to one preferred embodiment in accordance with the presentinvention, each auxiliary basemember is provided with ridge portionsdirectedperpendicularly to the axis of the tube, each ridge portionbeing disposed between two successive annular or ring members of thedelay line.

Referring now to the drawing, wherein like reference numerals are usedthroughout the various views to designate like parts, and moreparticularly to Figures l and 2, reference numeral 1 designates thereina metallic guide member also constituting the metallic cylindricalenvelope of a. forward wave amplifier tube, The cyl-indrical envelope 1is closed at the right end thereof, as viewed in Figure l, by anelectron collector element 2 of a propriate conventional constructionand at the other end thereof, by an insulating base 3 in which isdisposed the electron gun including an annular cathode 4, a heaterfilament 5, a focusing electrode 6 and an accelerating anode 7. Thecathode 4 is so constructed as to emit a `tubular electron beam 8. Thecathode 4 is carried at a negative potential with respect to theenvelope 1 by means of a conventional power supply or voltage source ofany appropriate construction and designated by reference numeral 9.

Coaxial metallic annular or ring-like members 1G are disposed in crosssections of the tube at right angles to the axis thereof. Each annularor ring-like member 10 is secure to the envelope 1 by two metallicspoke-like rod or support members 11 and 12 which are directed along adiameter of the annulus or ring as shown in Figure 2. The spoke-like rodor support members 11 and 12 which support the annular or ring-likemembers 10 are all parallel with respect to each other. In other words,successive support members 11 and 12 each form an aligned array,respectively, in an axial plane.

In addition, thereto, two auxiliary base members 13 and 14, constitutedby two metallic filler members, are secured to the inner wall of theenvelope 1 facing the free portions of the annular or ring-like members1G, i.e., in the spaces external of members 1b intermediate supportmembers 11 and 12 thereof. The base members 13 and 14 extend over theentire length of the extent of the annular or ringelike members 1t). Thecross sections of the members 13 and 14, in planes perpendicular toA theaxis of the tube, have the form of sectors of annuli. The assembly ofthe annular or ring-like members 10 and of the base members 13 and 14form, together with the envelope 1, the delay line of the tube. Thedelay line is coupled with the input circuit and output circuit of thetube by coaxial lines 15 and 16, respectively, which may be soconstructed in any suitable manner as to provide a proper impedancematch for a given band-pass or band-width with which the tube isdesigned to operate.

In the type of delay line in accordance with the present invention `andas described hereinabove, the high-frequency electric fieldperpendicular to each annular or ring-like member 10 is maximum alongthe free portions of the annulus or ring Whereas the high-frequencycurrents which circulate in each annular member are maximum in thesupport members 11 and 12 thereof. The electric fields of successiveannular or ring-like members 10 are coupled with each other as well asthe magnetic fields thereof produced by the circulating currents.Adjacent annular members 10, therefore, have both an electric andmagnetic coupling with one another. However, if the delay line did notinclude any auxiliary base members 13 and 14, the voltages induced bythese couplings would mutually oppose one another and the net resultantcoupling would, between the annular or ringlike members 10, be veryWeak. lt is known that under these conditions the delay line would havea very narrow band-pass. A Y Y The presence of the auxilitary basemembers 13 and 14 facing the external free portions of the annular orringlike members 10, that is, in the neighborhood of these portionswhere the electric field is maximum, reduces the electric couplingbetween successive annular members 10, and a portion of the electriclines of force are deviated toward the respective base member instead ofdirectly linking :the annularor ring-like members l@ with each other.Consequently, the magnetic coupling between annular or ring-like members10 is preponderant andthe annular or ring-like members 10 are therebystrongly coupled with one another. As a result thereof, the delay linepossesses a weak dispersion and a large band-pass.V Furthermore,calculations and experiments` both have conrrned that the upper cut-offfrequency of the band-pass is very high, `and therefore, the dangers ofparasitic oscillations by interaction with a backward space harmonic arevery slight. Moreover, the coupling impedance between the electron beamand the high-tref quency Wave is very high, with the electron beampassing at a very close distance from the line and being in interactionwith the fundamental wave in the delay line.

The delay line in accordance with the present invention is both sturdyand easy to manufacture. It possesses a high thermal dissipation, due tothe presence of the support members in contact with the metallicenvelope of the tube; Any thermal expansion is of little significance,for the delay line elements are so constructed as to be resistantagainstany torsional deformation. Furthermore, it is possible with aconstruction in accordance with the present invention to utilizesecuring support members which are more rigid than the annular orring-like members 10. Moreover, it is also possible to utilize, inconnection therewith, annular or ring-like membersl as Well asspoke-'like rod or support members which are of hollow circular crosssection to enable the circulation therethrough of any conventionalcooling Huid, such as water or the like.

The delay lines according to Figures 3 and 4 differ from `that ofFigures l and 2 only by the number of metallic rod or support membersfor the annular or ringlike members thereof and by the number of theauxiliary base members.

In the embodiment according to Figure 3, each annular,

or ring-like member 10 is securedto the metallic envelope 1 by a singleradial metallic rod or support member 17, the angular displacementbetween successive or adjacent support members 17 being again zero,i.e., again forming an aligned array in an axial plane. An aux-V iliaryelectrode or base member 18'of sector-like cross sec` tion is disposedalong the inner wall of the envelope 1 fac-4 ing the free portions ofthe annular member-s 10, and more particularly on the side thereofopposite the support members 17, Le., in the region where the electricfield is again maximum. K

ln the embodiment according to Figure 4, each annular or ring-likemember 1i) of the delay line is secured to the envelope 1 by threeradial metallic rod or support members 19, 20 and Z1 subtending an angleof 120 between cach other, the angular displacement between respectivesuccessive or adjacent support members being again zero, ie.,corresponding successive support members 19, 2li and Z1 each form analigned array in an axial plane. Three auxiliary base members 22, 23 and24 of sectorlike cross section are disposed along the inner wall of theenvelope 1 facing the free portions of the annular members 10, yoppositethe rods 19, 20 and 21.

A au,

The delay lines represented in Figures 1 through 4 allV possess a normaldispersion curve, that is, the fundamental space harmonic of the wavepropagated in these lines is direct.

A further improvement in accordance with the present invention consistsin providing along the surface of each auxiliary base member ridgesdirected perpendicularly to the axis of the tube, each ridge beingdisposed between successive annular or ring-like members V of the delayline. Figure 5 shows one embodiment of such improvement. The tubeillustrated therein is analogous to that of Figures 1 and 2, but eachbase member 13 and 14 is provided with ridge portions 31 and 32 disposedas shown in Figure 5.

The presence of the ridge portions 31 and 32 further reduces theelectric coupling between successive annular or ring-like members 10.This has as its result, as already indicated hereinabove, a decrease inthe dispersion of the delay line and, therefore, an increase in thewidth of the band-pass of the tube.

It is understood that the present invention is not limited to theembodiments described and shown herein but is susceptible of manychanges and modifications within the spirit of the present invention,for example, delay lines having a normal dispersion curve might alsoinclude more than three auxiliary base members and more than threesupport members, the number of the auxiliary base members .and of thesupport membersbeing equal, and I, therefore, intend to cover all suchchanges and modifications within the scope of the present invention asencompassed by the appended claims.

`I claim: j i

l. In a forward wave amplifier tube, a delay line co prising a series ofseparate metallic ring-like members lmutually spaced from each other so.asto for-m individual supporting each of said members within said guideexclusive of the next adjacent member and conductive segment-likemembers secured to the inside of said guide and extending intermediatesaid support means over the length of said line.

2. In a forward wave amplier, the combination according to claim l,wherein said support means consists of at least one array of alignedsupporting rods.

3. In a forward wave amplifier tube, a `delay line comprising a seriesof unconnected metal rings mutually spaced along a common axis, a guidemember having ya metallic cylindrical surface coaxially surrounding saidrings, at least one radial metallic rod supporting each of said rings onsaid surface, said supporting rod of each `one of said rings beingaligned to form an array in an axial plane with supporting rods ofadjacent rings, the number of said rods in'said array being equal to the',for each of said metallic ring-like members for individually number ofsaid rings, and at least one metallic filler member having a form of acylindrical segment, said segment extending essentially axially oversaid series of rings in the space between said cylindrical surface of`said guide member and the external surface of said rings,

and being secured to a portion of said cylindrical surface outside thefixation point of said rods on said cylindrical surface.

4. A delay line as claimed in claim 3, wherein each ring is supported bya single rod, said filler member being fixed to a portion of saidcylindrical surface opposite the fixation point of said rod on saidsurface.

5. A delay line as claimed in claim 3, wherein each ring is supported bya plurality of symmetrically distributed rods aligned to form acorresponding number of said arrays, there being provided the samenumber of said ller members, and each of said members being fixed to aportion of said cylindrical surface between adjacent arrays.

l6. A delay line as claimed in claim 5, wherein each ring is supportedby a pair of oppositely directed rods, two filler members being fixed toopposite portions of said surface and having a plane of symmetry atright angles to said rods.

7. A delay line as claimed in claim 5, wherein each ring is supported bythree rods mutually shifted by three filler members being clixed tothree portions of said sur-face mutually shifted by 120 and having planeof symmetry shifted by `60 with respect to adjacent rods.

8. A delay line as claimed in claim 3, further comprising transverseridges provided on said. ller members.

9.- A delay line as claimed in claim 8, wherein each transverse ridge issymmetrically positioned between a pair of adjacent rings.

10. A forward wave amplifier tube having a delay line comprising aplurality of unconnected metal rings mutually spaced along a commonaxis, a metallic envelope having a cylindrical surface essentiallycoaxially surrounding said rings, at least one essentially radiallydisposed metallic rod supporting each of said rings on said surface, thesupporting rod for each one of said rings being aligned to form an arrayin an axial plane with supporting rods of adjacent rings, the number ofsaid rods in said `array being equal to the number of said rings, and atleast one metallic filler lmember having the shape of a cylindricalsegment, said segment extend- Y ing essentially `axially over saidseries of rings in the space between said cylindrical surface of saidguide member and the external surface of said rings, and being securedto a portion of said cylindrical surface outside the xation points ofsaid rods on said cylindrical surface.

References Cited in the file of this patent

